Am I missing something

[70bigblockdodge]

Problem on my Challenger. I have been fiddling with the tune on this car for a while.
Low compression 400 with cut down 516 casting heads @73cc, compression calculates out to 8.46:1
With a 284/484 Mopar cam
Wiend aluminum intake and headers
I have a lean spot in the RPM range idle to about 3300-3500
Engine has about 11" hg in park 1200 RPM and drops off to 8" in gear, I have played around with timing idle settings power valve.
So checking for vacuum leaks I found one in the hose to vacuum booster so I changed it no difference, plugged the port eliminating the booster no change, tried to draw a vacuum on the booster and I cannot get it to draw one. Reconnected booster ran engine at high idle 15" plus vacuum them **** off car and reconnect gauge and pump it sucked right to over 15"". My booster seems to work fine except for the bad vacuum from cam (you don't get multiple pumps at idle)
I think my little hand vacuum pump should still be able to pull a vacuum on the booster or maybe it is just a POS. I do not think the booster is bad but now it has me second guessing my self.

 

[jake]

I know i could not pull a vacuum on my booster with my hand pump, no matter how long I worked at it, and my booster is good.

 

[pomonamissel]

thats to much cam for that cr level , and mine made about 15 inches of vac at idle . have you degree'd that cam ? and do the math for dcr with that cam your numbers are going to be very low .

 

[Yatzee]

Problem on my Challenger. I have been fiddling with the tune on this car for a while.
Low compression 400 with cut down 516 casting heads @73cc, compression calculates out to 8.46:1
With a 284/484 Mopar cam
Wiend aluminum intake and headers
I have a lean spot in the RPM range idle to about 3300-3500
Engine has about 11" hg in park 1200 RPM and drops off to 8" in gear, I have played around with timing idle settings power valve.
So checking for vacuum leaks I found one in the hose to vacuum booster so I changed it no difference, plugged the port eliminating the booster no change, tried to draw a vacuum on the booster and I cannot get it to draw one. Reconnected booster ran engine at high idle 15" plus vacuum them **** off car and reconnect gauge and pump it sucked right to over 15"". My booster seems to work fine except for the bad vacuum from cam (you don't get multiple pumps at idle)
I think my little hand vacuum pump should still be able to pull a vacuum on the booster or maybe it is just a POS. I do not think the booster is bad but now it has me second guessing my self.

You may want to take a look at the advance curve for your distributor. Had a similar problem and changed the max lockout points for my mechanical advance. I did not have to change the springs. You may have to if their too light. Thing runs like a beast with 16 degrees base timing and 16 degrees mechanical. I run a 3200 - 3400 stall convertor.

 

[70bigblockdodge]

You may want to take a look at the advance curve for your distributor. Had a similar problem and changed the max lockout points for my mechanical advance. I did not have to change the springs. You may have to if their too light. Thing runs like a beast with 16 degrees base timing and 16 degrees mechanical. I run a 3200 - 3400 stall convertor.

I'm at 25° initial 36 total, I welded the slots up for only 11° of advance, car drives much better. I am almost positive the main circuit is not working properly due to vacuum and air speed a problem that could be corrected with a converter and gears, next plan is a converter swap gears will stay I'm not killing the highway in the car. I just got caught up in this booster issue and wanted a opinion, I think I did something wrong checking it.

 

[70bigblockdodge]

thats to much cam for that cr level , and mine made about 15 inches of vac at idle . have you degree'd that cam ? and do the math for dcr with that cam your numbers are going to be very low .

Yeah I agree but this was just a freshen and go have some fun. The low vacuum does not bother me and with a 3.5hg power valve the idle cleaned up. I'm pretty sure the converter will get me out of the basement RPMs and improve drivability and 1/4 time. I did not degree the cam just checked TDC against the marks I may go back in and advance it to cope with compression and I really don't need to spin cast pistons much above 6000.
I guess I will have to go look at FSM and follow it to see if booster is a problem.

 

[pomonamissel]

needs a 4spd , lol .

 

[70bigblockdodge]

needs a 4spd , lol .

That was tempting if my Charger didn't already have one and I might be in the hunt for a manual brake push rod for a E body at Carlisle.

 

[pomonamissel]

think i got one from a 70ish challenger still on the peddles . whats the length ?

 

[70bigblockdodge]

I'm not sure I will check my Brother in law's parts book when I get over there, or I'll just measure his on his Cuda.

 

[pomonamissel]

no issues here , take your time .